Replacing crystalline lenses with implants has become a common operation in the field of eye surgery.
One of the problems that arise after such surgery is the impossibility of focussing both near and far when a monofocal intraocular lens is used, as the lens is fixed within the capsular bag and only one focal point can be chosen, so that the use of external lenses is necessary.
Instead, multifocal intraocular lenses provide two or more focal points, thereby avoiding the need for external lenses as they allow correcting vision at all distances.
However, multifocal intraocular lenses present drawbacks such as lack of clarity and perception of halos around light sources, among others.
These drawbacks have encouraged studying the implantation of accommodative lenses, which are lenses with a single focal point that operate as multifocal intraocular lenses since they are designed with an articulation similar to the mechanics of the crystalline lens, such that the action of the eye muscles allows changing the single focal point in order to focus objects at different distances.
Regarding the accommodation mechanisms, it has been found that the eye undergoes certain changes such as pupil contraction, contraction of the ciliary muscle, relaxation of the zonular ligament and changes in the size of the lens, such as increased thickness and curvature of its anterior face.
There exist several theories for explaining the physiological mechanism of accommodation, among which are those of Helmholtz, Tscherning, Gullstrand and Pflugk, wherein one of the most relevant factors is the action of the ciliary muscle on the eye, the crystalline lens and the incurving of its anterior face.
It is important to point out that the capsular bag is very elastic, as when it breaks it retracts such that the tear increases in size, and the folds that appear when the capsular bag is empty disappear completely when it is expanded.
After the crystalline lens has been removed the posterior capsule is left loose, as the anterior capsule is open, so that its effects on the eye are eliminated; the posterior capsule can even advance farther in an anterior direction as the anterior capsule is not retaining it.
This is observed in interventions on the crystalline lens, and occasionally the posterior capsule suffers a hernia due to capsulotomy when the posterior vitreous pressure increases.
The possibility of using a lens to replace the functions of the crystalline lens would bring us closer to a true accommodation.
A desirable optic for accommodation is one that deforms in response to a force applied on the equator of the optics.
Under the influence of this force, the optic will bulge out in an axial direction, so that the posterior and/or anterior faces will increase their curvature and therefore increase the accommodation capability of the optic. This is, the greater the capability of a lens to deform the optics the greater its accommodation capability.
Numerous implants have been designed that attempt to use the contraction and relaxation of the ciliary muscle to modify the optical capability of the eye.
In general, intraocular lenses comprise an optical part that ensures optical and particularly refractive correction and a haptic part that allows the optic to move.
Patent US2002/0138140 Al uses a flexible annular device that deforms upon contraction of the ciliary muscle, the design of which is meant to allow the movement of the lens haptic and exert the action of the ciliary muscle to favour accommodation, which is reflected in the figures describing a posterior distension of the posterior capsule.
However, the design of the intraocular lens of patent US2002/0138140 Al does not allow using the capsular distension at any time as a mechanism for amplifying the motion, nor does it modify the curvature or thickness of the optic.
U.S. Pat. No. 666,003B1 describes a system of levers wherein some branches pivot about others, increasing accommodation by converting the radial movement of the capsular bag into a movement of axial amplification of the optic, where the haptics or ring are designed such that they are flexible, to allow the ciliary muscle to transmit the contraction; however, its design does not allow moving the haptics, so that it cannot achieve maximum distension of the capsular bag.
Therefore, a need exists for an intraocular lens comprising means that allow both moving the optic and a greater deformation of the anterior and/or posterior deformation of the optic, thereby resulting in a greater accommodation capability.